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Old May 11, 2009, 5:29 PM   #1
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Default Full/Croped sensor lenses?

I curenly have a Rebel XT, and I use a EF-S 17-85mm f/4-5.6 IS, and a EF 50mm f/1.8. I know it's nothing fancy but it was enough to get me very interested in photography. I've recently been doing alot a reading and compiling my wish list, of a 5D and 3 lenses. There's one question I haven't been able to answer myself so I'm asking here in hopes someone can help me out.

Is there a difference in lenses for a croped sensor camera and a full frame camera? Now my ultimate goal is to start shotting weddings full time once I learn to do it properly. It was suggested I get a 70-200 f/2.8 IS, a 24-105 f/4 is, and a wide angle lens. BUT if I was still shotting with a croped sensor to get 17-55mm f/2.8 IS.

If my previous questiion's answer was yes, then I ask. Will a croped sensor lens still work on a full frame, and what would change in it? And would a full frame lens still work on say my Rebel XT if I decide to get the lenses first?
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Old May 11, 2009, 9:00 PM   #2
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The larger the sensor or film size, the wider the angle of view for any given focal length. The smaller the sensor or film size, the narrower the angle of view for any given focal length. With your Rebel XT, you can multiply the focal length of a lens by 1.6x to see what focal length lens you'd need on a 35mm camera for the same angle of view (apparent magnification).

For example, when you use a 17-85mm lens on a Canon dSLR with an APS-C size sensor, you'll have the same angle of view you'd have using a 27-136mm lens on a 35mm camera (or Canon dSLR with the same size sensor like an EOS-5D).

No, you can't use the 17-85mm on a camera with a larger sensor or film size. It's an EF-S mount lens that's specifically designed for cameras with an APS-C size sensor, and the image circle it projects isn't large enough to cover a larger sensor without vignetting. You'll need to stick with EF (not EF-S) mount lenses for a 5D.

However, you can use an EF mount lens like your 50mm f/1.8 on either camera model. It will have a narrower angle of view (more apparent magnification) on the Rebel XT compared to using it on a model like a 5D with a larger sensor.

The same thing would apply to the 24-120mm. It could be used on either camera type. But, if you use it on the Rebel XT, you'd have the same angle of view you'd have using a 38-192mm lens on 35mm camera (or a dSLR model with the same sensor size like a 5D). Ditto for the 70-200mm (it will work on either camera type, but you'll have a narrower angle of view with it on the XT versus a 5D).

The narrower angle of view you have with a camera using an APS-C size sensor is one reason most kit lenses tend to start out at around 17 or 18mm (since you can only back up so far in many conditions, and you may not be able to fit your subject into the frame if you use a lens starting out too long).
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Old May 12, 2009, 12:04 PM   #3
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That's more then I was expecting, and answered so much. Thank you so much for this.
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